Telephone relay connection



Aug. 6, 1929.

F. ALBRECHT TELEPHONE RELAY CONNECTION Filed Febl 26, 1924 T If? Inventor: Fritz Al brecht,

His Attorney.

Patented Aug. 6, 1929.

UNITED STATES PATENT oFFICE.

FRITZ ALBRECHT, OF CI-IARLOTTENBURG, GERMANY, ASSIGNOB T0 GENERAL ELEC- TRIC COMPANY, A CORPORATION OF NEW YORK.

TELEPHONE RELAY CQNLTECTION.

Application filed February 26, 1924, Serial No. 695,345, and in- Germany April 24, 1923.

My present invention relates to connections for telephone relays or amplifiers, and more particularly to connections which are especially adapted for use with amplifiers connected in long distance lines.

In cases where amplifying relays or repeaters, particularly of the electron discharge type are used in long distance telephone lines, it becomes inconvenient at times to select a suitable location for the housing of the apparatus. It may happen that in the most suitable location for the apparatus the only current available is alternating current. In such a case it is necessary to rectify the alternating current to supply the required storage batteries for the plate circuits and the provision of the batteries themselves requires a large expense both for the original installation and for its maintenance.

The object of my invention is to provide a connection whereby the installation of batteries for providing the plate potential at an intermediate point on a long distance line will be unnecessary. This object is accomplished by superimposing upon the long distance line at a terminal station a steady unidirectional potential of the value necessary for operating the plate circuits of the relay or relays connected in the line. The necessary direct current supply may be transmitted over the long distance line without interfering in any way with the speech communication.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. hIy invention itself, however, both as to its organization and method of operation will best be understood by reference to the following description taken in connection with the accompanying drawing in which I have indicated diagrammatically one, Way in which my invention may be carried into effect.

I have indicated in the drawing the connection of an amplifier or relay of the electron discharge type at an intermediate point in the long distance line. The incoming line to the relay 1 comprises conductors 2 and the outgoing line the conductors 3. At one of the terminal stations of the line the necessary potential for supplying the plate or output circuit of the amplifier 1 is impressed between the two line conductors.

Speech currents coming in over the line conductors 2 are impressed by means of the transformer 4 upon the input circuit of the relay 1, and the amplified speech currents are impressed by means of the transformer upon the conductors 8 of the outgoing line. lVith the connections shown it is assumed that a steady undirectional potential is impressed between the conductors 2. The blocking condenser 6 prevents direct current from flowing through the primary of the transformer 4t. The positive potential for the plate sup ply of the amplifier 1 is provided by a connection 7 which is connected to the intermediate point- 8 in a choke coil 9, one terminal of this choke coil being connected through the primary of transformer 5 to the plate or anode 10 of the relay. The condenser l1 furnishes a path for the speech currents flowing in the output circuit of amplifier 1. The second terminal of choke coil 9 is connected at 12 to one side of the outgoing line 3 so that the high potential undirectional voltage may be supplied over the outgoing line 3 to other relays which may be inserted in the long distance line. the condenser 13 furnishes a path for the speech currents, but prevents the flow of direct current through the secondary of transformer 5.

The choke coil 9 is preferably so designed that it offers a very high impedance to currents of the speech frequency. This is essential in order that the feed-back furnished by the connection 7 will not be suili cient to cause the production of oscillations. It is also possible, assuming that the natural frequency of the line is considerably higher than the frequency of the ringing current employed, to so design the choke coil 9 that it will permit the ringing current to pass through and at the same time have a strong choking action for speech currents and currents of the natural frequency of the line. It is then also possible by means of this choke coil to send a ringing current over the entire line without any necessity that it shall pass through the amplifier.

It is apparent that in place of the simple choke coil 9 for the described purpose, it is also possible to use filters of any well known form. These would have the advantage that the desired result would be obtained with less resistance. The ringing current would,

when flowing past the amplifier, meet with less resistance than is the case when using the choke coil as illustrated.

While it is comparatively easy to transmit over the telephone line the current necessary for operating the plate circuit of the amplificr, the transmission of the current required for the heating of the cathode 14 of the amplifier presents greater 'diiiiculties. If an amplification entirely independent of local operating current sources is to be ol tained it is possible to use for this purpose gas discharge relays such as described in German patent to Schroter, 299,654. The provision of the necessary storage batteries for heating the cathode of the amplifier, however, does not present so great a difliculty because of the fact that low voltage only is required and hence the extent of the installation and the difliculties of keeping them charged is much less than when it necessary to provide storage batteries for the plate supply as well.

While I have shown and described the preferred embodiment of my invention, it is apparent that many modifications in the connections and apparatus employed may be made without departing from the scope of my invention as set forth in the appended claims.

hat I claim as new and desire to secure by Letters Patent of the United States, is

1. The combination with a long distance telephone line of a relay having input and output circuits located at an intermediate point in said line, means for supplying alternating currents from said line to the input circuit of said relay, means for supplying over said line and from a point in said line distant from said relay a steady unidirectional potential to the output circuit of said relay, means included in the connection for supplying the potential to the output circuit for preventing a feed-back of alternating current energy from the output circuit to the input circuit, said means comprising a choke coil which prevents the passage therethrough of talking currents but permits the passage of low frequency calling currents.

2. The combination with a long distance telephone line of a relay having input and output circuits located at an intermediate point in said line, a transformer for supplying talking currents from said line to said input circuit, a second transformer for supplying talking currents from said output circuit to said line, means for supplying over said line and from a point in said line distant from said relay a steady unidirectional potential to said output circuit, and means for preventing the How of direct current through the primary winding of the first transformer.

3. The combination with a long distance telephone line of a relay having input and output circuits located at an intermediate point in said line, a transformer for supplying talking currents from said line to said input circuit, a second transformer for supplying talking currents from said output circuit to said line, means for supplying over said line and from a point in said line distant from said relay a steady unidirectional potential to said output circuit, means for preventing the flow of direct current through the primary winding of the first transformer, and means for preventing a feed back of alternating current energy from the output circuit to the input circuit.

at. The combination with a long distance telephone line of a relay located at an intermediate point in said line, and having input and output circuits connected thereto through transformers, a choke coil connected between one side of the outgoing line and the output circuit and a connection from one side of the incoming line to an intermediate point in said choke coil.

5. The combination with a long distance telephone line of a relay located at an intermediate point in said line, and having input and output circuits connected thereto through transformers, a choke coil connected between one side of the outgoing line and the output circuit and a connection from one side of the incoming line to an intermediate point in said choke coil, said choke coil being so designed as to permit the passage of low frequency calling currents but to ofier a high impedance to talking currents.

In Witness whereof, I have hereunto set my hand this 24th day of January, 1924:.

DR. FRITZ ALBRECHT. 

